One example of a data communication network in which the invention can be used is EGPRS or GPRS, in which a so-called link layer protocol context (TBF) is set up between a transmitting network site and a receiving network site and in which a further link layer protocol context (TBF) is set up for the data transmission from the second network site to the first network site. This link layer protocol context is called Temporary Block Flow (TBF) in GPRS and EGPRS.
If a TBF in EGPRS or GPRS has been set up, a scheduler assigns the necessary radio resources for transmitting a single data packet via the air interface. As will be briefly explained below, typically in TCP data transmission, each data transmission in one direction is confirmed by an acknowledgement transmission in the reverse direction and each direction needs the setting up and tearing down of a TBF. The setting up and tearing down of the TBF is conventionally controlled by the number of data packets to be transmitted.
The setting up and tearing down of a TBF requires a large amount of signalling between the two network sites and thus there may be quite a substantial delay when data packets or acknowledgement information is to be transmitted and a TBF has not been set up already. Furthermore, since the only criterion which causes the setting up of a TBF is the number of packets to be transmitted, there may occur a situation where after transmission of a few data packets the TBF is cancelled and has to be set up again if after only a short period of time a new set of data packets is pending to be transmitted. Alternatively, if the TBF was just kept open unconditionally, i.e. even in cases where no acknowledgment or data packets need to be transmitted, this would cause a substantial waste of resources. The present invention aims to reduce this waste of transmission resources and in particular the invention aims to reduce delays during the transmission due to unnecessary TBF set up and tear down procedures.
FIG. 1a shows a typical data communication network SYS comprising a first network site, for example a base station system BSS, and a plurality of second network sites, for example a plurality of mobile stations MS, MS′, MS″. As explained above, typically there is a downlink DATA-DWN, on which a data transmission from the first network site BSS to the second network site MS occurs if simultaneously the downlink layer protocol context TBF-DWN is established. Likewise, if an uplink layer protocol context TBF-UP is established, a transmission of data can occur on an uplink DATA-UP. That is, for each transmission direction a link layer protocol context TBF must be established.
A well-known protocol for such data transmissions is TCP, which provides connection-oriented services for the application layer of the Internet protocol. A transmitting network site and a receiving network site establish a connection in order to exchange data and TCP transmits data in segments, which are encased in IP datagrams. Check sums are used to detect data corruption. In addition, sequence numbers ensure an ordered byte stream.
As shown in FIG. 1b, in TCP each data transmission ST1, ST3, . . . between a TCP host and a TCP terminal requires the receiving network site, i.e. the TCP terminal, to acknowledge the receipt of data by returning acknowledgements ST2, ST4 to the transmitting site, i.e. to the TCP host. This acknowledgement confirms the receipt of data and its completeness. Since each data transmission is confirmed with an acknowledgement re-transmission TCP is considered to be a very reliable transport mechanism, in particular for large data streams. If the transmitting site does not receive an acknowledgement information from the receiving site within an expected time frame, the segment (IP datagram) is re-transmitted. It should be noted that TCP-IP as explained above is only one example of a protocol where a transmission of acknowledgments is performed. The present invention, however, is not limited to TCP-IP. For example, it may even be applicable to UDP, i.e. for constant stream arrival.
FIG. 1c in connection with FIG. 2 shows the general data transmission of FIG. 1b on a more detailed protocol layer. In FIG. 2, showing the protocol stack of a typical GPRS system, the nodes SGSN and GGSN as well as the base station system BSS can be considered to belong to the host site whereas the terminal MS can be considered to belong to the terminal site. Independently as to what kind of “data” is transmitted from the TCP host to the TCP terminal in step ST14 in FIG. 1c (it can be real user data or acknowledgement data) and independently as to what kind of data is transmitted from the TCP terminal to the TCP host in step ST24 (the data can be real user data or acknowledgement data), the downlink transmission and uplink transmission, respectively, require the set-up of a TBF in operations ST13 and ST23, respectively, after TCP packets forwarded in the respective steps ST11, ST21 have been encapsulated in LLC frames at the IP in steps S12 and S22, respectively. The TBF is set up between the respective RLC layers of host and terminal as indicated with the steps ST13, ST23. After de-encapsulation from the LLC frames in steps ST15, ST25 the TCP packets are forwarded to the receiving site in steps ST16 (to the TCP terminal) and ST26 (to the TCP host). For example, step ST11 could involve the transmission of data in the downlink direction from the host to a terminal whilst in step ST26 acknowledgement data is returned from the terminal to the host.
FIG. 3 and FIG. 4 respectively show how the link layer protocol context TBF is established between the RLC layers. After steps S31, S32 (in FIG. 3) and steps S41, S42 (in FIG. 4) the respective downlink and uplink TBFs are set up. Then data transmission is possible in steps S33, S43, which is followed by acknowledgement transmissions in step S34, S44.
If after step S35 in FIG. 3 there are no more RLC segments from the transmitting site, there is the possibility that a timer keeps the TBF open for a certain time period and after step S36 the TBF is released on the transmitting site.
Similarly, during the uplink data transmission, a final acknowledgement information is re-turned in step S46 from the transmitting site BSS to the receiving site MS indicating that the uplink TBF should be released on the receiving site MS. Then, after step S47 the TBF is also released on the transmitting site BSS. More particularly, in FIG. 4 each uplink data transmission in step S43, S45 includes an indication CV of the number of remaining data packets to be transmitted from the terminal site MS and if there are no further data packets to be transmitted (CV=0 or CV≦15), the teardown procedure for the uplink TBF is started. FIG. 3 and FIG. 4 may be respectively viewed as the “TBF-DWN establishment” and “TBF-UP establishment” in steps ST13 and ST23 in FIG. 1c. 
Thus, as shown in step S1 in FIG. 5a, a transmission reception unit TR/RC of the transmitting site (BSS or MS) receives/transmits data packets (downlink data transmission: DATA in downlink/acknowledgement in uplink; uplink data transmission: DATA in uplink/acknowledgment information ACK in downlink). As explained with reference to FIG. 3 and FIG. 4, the set up and teardown procedures for the respective TBF are only governed by the fact whether or not data packets are pending to be transmitted. For example, if the CV value (the value which indicates the remaining number of packets) gets smaller than 15, the TBF tear down procedure cannot be stopped any more.
Furthermore, of course a data transmission between a transmitting site and receiving site can only take place if sufficient radio blocks are available and have been assigned to the respective uplink and downlink transmission. That is, if there are packets to be transmitted, in step S2 a resource allocater ALLO (shown in FIG. 5b) assigns the necessary radio resources for the packet transmission. In GPRS, the BSS decides for the uplink as well as for the downlink direction, which control channel or data channel is used and which terminal MS (MS′, MS″) can use it. The BSS controls the access on the uplink PDCH (packet data channel) via a so-called Uplink State Flag USF and the so-called Relative Reserved Block Period RRBP in the header of the radio blocks. The USF in the downlink radio block indicates which terminal is allowed to use the corresponding radio block slot in the uplink direction. The mobile station or terminal receiving the downlink block can be different from the mobile station indicated by the USF for the uplink direction, i.e. every terminal MS listening on the PDCH reads the USF flag.
As may be understood from the above explanation, in data communication systems in which a link layer protocol context TBF needs to be established in the uplink direction and downlink direction for respectively transmitting data and acknowledgement information, a TBF has to be set up respectively in the uplink and downlink direction and resources are allocated by the first network site BSS (steps S1, S2 in FIG. 5).
However, the set up, the maintaining and the tearing down of TBFs and the allocation of radio resources (radio blocks) is only governed by the fact how many data packets are pending to be transmitted at a particular point in time from a transmitting site. For example, if in FIG. 1c a number of acknowledgment packets are pending to be transmitted from the TCP terminal to the TCP host (on the uplink direction) in response to one or more data packets having been transmitted from the TCP host to the TCP terminal (in the downlink direction), the uplink TBF in step ST23 may be teared down after the last transmitted acknowledgement packet whilst there are still many more data packets being transmitted in the downlink direction. Thus, if a next acknowledgement data packet has to be transmitted in the uplink direction, the TBF has to be set up again, which causes an unnecessary overhead signalling and delay. The repeated set-up of a TBF could be avoided if the TBF was kept open (set-up) for a predetermined period of time to allow a transmission of acknowledgments at any time. However, this would cause an unnecessary waste of transmission resources.
As may be understood from this explanation, whilst the data packet transmission on the downlink and the downlink are quite clearly correlated, i.e. each data packet transmission in one direction is confirmed with an acknowledgement data packet transmission in the reverse direction, the actual adjustment of the radio resources is only made on the basis of pending data packets to be transmitted.